1. Technical Field
This invention relates to a power converter for a vehicle.
2. Related Art
A known power converter includes a power supply unit for an electrical vehicle as disclosed in Japanese Patent Application Laid-Open Publication No. H7-087601.
The disclosed power supply unit for an electrical vehicle, which includes an activation circuit, a transformer, a switching circuit, and a rectifying-smoothing circuit, is activated upon turn on of a main switch, isolates and steps down a high direct-current (DC) voltage of a main power supply (power supply for travelling), and supplies the stepped down voltage to an accessory power supply of low DC voltage. The main power supply supplies the high DC voltage to a traction motor. The accessory power supply supplies the low DC voltage to a control unit or a vehicle light or the like.
Upon turn on of the main switch, the activation circuit connects the main power supply to the switching circuit to activate the switching circuit, and connects the main power supply to the transformer. The switching circuit is activated upon application of the high DC voltage of the main power supply to the switching circuit, converts the high DC voltage into an alternate-current (AC) voltage through switching of the switching circuit, and supplies the AC voltage to a primary winding of the transformer. The transformer isolates and steps down the AC voltage applied to the primary winding of the transformer, and outputs the stepped down AC voltage from a secondary winding of the transformer. The rectifying-smoothing circuit converts the stepped down AC voltage outputted from the secondary winding of the transformer into a low DC voltage to supply the low DC voltage to the accessory power supply.
That is, in the disclosed power supply unit for an electrical vehicle, the main power supply is electrically connected to the switching circuit via the activation circuit to activate the switching circuit. Thereafter, the main power supply is electrically connected to the transformer, where the AC voltage converted from the high DC voltage by the switching circuit is isolated and stepped down to supply to the low DC voltage to the accessory power supply through the rectifying-smoothing circuit.
However, the disclosed power supply unit for an electrical vehicle has a disadvantage that since the switching circuit is activated upon application of the high DC voltage of the main power supply, a component of the switching circuit to which the high DC voltage is applied has to withstand high-voltages. This leads to an increase of manufacturing costs.
There is another kind of power supply unit for an electrical vehicle, where a switching circuit is activated upon application of a low DC voltage of an accessory power supply to the switching circuit. Such a power supply unit for an electrical vehicle, however, has to include an activation circuit that connects the accessory power supply to the switching circuit upon turn on of a main switch to activate the switching circuit, where information about a state of the main switch has to be conveyed to the activation circuit. Hence, a length of a wiring for conveying the information about a state of the main switch is increased with a longer distance from the main switch to the activation circuit, which leads to an increase in manufacturing costs.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a power converter capable of activating a control circuit without increasing a length of a wiring for conveying an activation signal, where the control circuit is activated when electrically connected to a low voltage power supply in response to the activation signal.